As you already know, most of Breaking Dawn filming is going to be taking place in Baton Rouge, Louisiana. And it looks like work is already starting down there. According to Malicious Mandy:

I got an email over the weekend from a fellow Twilight fan in Baton Rouge. Here are some details she sent me regarding Pre-Production of Breaking Dawn:

•studio is secure and gated but busy.
•a lot of construction going on in the lots (unsure if related to filming or not, it seems likely)
•they are using the lot across from studio also (for storage and vehicles at this point)
•Bill Condon has been spotted in town and is staying at a private location not too far from studios

Baton Rouge is extremely excited for the economical boost that Breaking Dawn filming is bound to give them. According to local news channels:

Whether or not "Twilight's" last installment, "Breaking Dawn," is coming to Celtic, the studio says big bucks follow big projects.

"Each production is like a small army, so you're having to feed a small army, you're having to house them, you're having to entertain them," said Mulhearn.

In the case of "Twilight," Baton Rouge will also benefit from the twi-hards.

"What you'll see is much like what 'Steel Magnolias' did for Natchitoches," said Stelly. "People go to Natchitoches to this day to see the house in 'Steel Magnolias.'"

The Baton Rouge area is counting on it.

"'Twilight,'" said Stelly, "it's gonna be a great addition to our cannon."